Disk drives are known in the art that use various kinds of disks, such as: optical disks, magneto-optical disks, flexible magnetic-recording disks, and similar disks of data-storage devices. In particular, hard-disk drives (HDDs) have been widely used as indispensable data-storage devices for computer systems. Moreover, HDDs have found widespread application to motion picture recording and reproducing apparatuses, car navigation systems, cellular phones, and similar devices, in addition to the computers, because of their outstanding information-storage characteristics.
In standard HDDs, a rotary actuator having a magnetic-recording head mounted at one end is driven in rotation about a pivot shaft of the rotary actuator; and, by this means, the magnetic-recording head can be positioned at any radial position over a magnetic-recording disk so that writing data to, and reading data from, the magnetic-recording disk can be performed. A voice coil is mounted at the other end of the rotary actuator, and the drive force for rotating the rotary actuator is produced by means of a voice-coil motor (VCM), which includes a VCM magnet that is secured to the disk enclosure (DE) of the HDD. The VCM has a structure in which the voice coil is disposed between yokes made of a soft magnetic material in order to form a magnet for generating magnetic flux and a magnetic circuit.
Against the background of the “information society”, in which there is a need for greater information-storage capacity in HDDs, attempts are being made to improve the positioning accuracy of magnetic-recording heads and to produce HDDs which are able to record at higher areal density by reducing vibration excitation forces inside HDDs and attenuating disturbances, which have larger affects as the control bandwidth of the rotary actuator increases with the demand for higher areal density. Conventional mechanisms for positioning rotary actuators are those in which the magnetic-recording head at the distal end of the rotary actuator is driven in rotation and placed in a specific position by applying a voice-coil current to the voice coil of the VCM. Increases in the control bandwidth in head positioning systems involving a VCM has been achieved by making the rotary actuator more rigid, which increases the main resonance frequency, because the control bandwidth stems largely from the main resonance frequency of the rotary actuator. However, even larger increases in the control bandwidth are difficult to achieve by further increasing the rigidity of the rotary actuator. Therefore, efforts have been made to reduce the phase lag produced by the filter of the hard-disk controller (HDC) for attenuating resonance in order to maintain stable control, by reducing out-of-plane structural resonance, such as torsional resonance and bending resonance. In view of this, structures for attenuating structural resonance have been proposed in the art, as next described.
In a first example known in the art, a structure for minimizing track-positioning errors of the magnetic-recording head that are caused by dynamic mechanical deformation of the HDD suspension and magnetic-recording head provides an attenuation mechanism on the voice coil and voice-coil support part. However, the HDD including the attenuation mechanism on the voice coil and voice-coil support part does not include a structure which reduces the actual excitation force of the resonance in the VCM.
In a second example known in the art, a HDD includes two voice coils in parallel in the lengthwise direction of the rotary actuator, and includes a VCM that does not induce main resonance that adversely affects the increase in control bandwidth. In the track following mode for positioning the magnetic-recording head at a specific track on the magnetic-recording disk, current is applied to the second voice coil; while in the track seek mode for moving the magnetic-recording head to a specific track, current is applied to the first voice coil. Moreover, the two voice coils are not parallel to the pivot shaft of the rotary actuator, and current is only applied to one of the voice coils in each of the two modes.
In a third example known in the art, in order to increase the bandwidth of the rotary actuator in a HDD, the HDD may employ two modes, namely a track following mode for positioning the magnetic-recording head and a track seek mode for moving to a specific track; and, the voltage is divided between two voice coils during track following for positioning the magnetic-recording head, such that the main resonance frequency that adversely affects increases in control bandwidth is not excited. The orientations of the currents applied to the two voice coils in the track following mode are opposing, and therefore the rotational moment generated per unit current is reduced, and a large current is required, which leads to increased electrical power consumption.
These designs suggest that engineers and scientists engaged in HDD manufacturing and development have an on-going interest in the design of HDDs that control the motion of the rotary actuator that bears the magnetic-recording head in accessing data written to, and read back from, the magnetic-recording disk to meet the rising demands of the marketplace for increased data-storage capacity, performance, and reliability of HDDs.